M Dwarf Exoplanets

One of the interesting scientific discoveries of the past decade has been that there are planets orbiting other stars (called exoplanets) and that many of these planets may have temperatures that would allow liquid water to exist on their surfaces. There has been a special interest in M dwarf exoplanets.

In theory, all stars could have a possible planet in a zone where the temperatures would be between zero and 100 degrees Celcius. However, that zone could be very small, and there are many factors required to make life possible, and many that would make life impossible. In an article in Science News dated June 24, 2017, (page 18) some of those factors were mentioned. They include stellar flares, gravitational locking, and especially the life expectancy of the star.

Stars age and the period during which their habitable zone could exist in a stable form is very short. M dwarf stars are held up as having long enough lifetimes for water to exist and biological processes to take place. Since they are the most common type of star in the Milky Way (70% of all the stars in our galaxy) scientists are studying them closely. We have reported before on one of them called TRAPPIST-1.

As more data comes in, it is becoming apparent that although M dwarf exoplanets remain as they are for very long times, they are still not stable enough to sustain life. Scientists hoping to find another “earth” orbiting another star are learning that M dwarfs are not good candidates even though they have some of the conditions necessary for life.